Telling it like it is: Spalding Gray performing a monologue on stage in New York in 1999. Photo: Sara Krulwich, AP

With the 1985 film Swimming To Cambodia, the singular personality of the performance artist Spalding Gray, who has died aged 62, transformed the art of the monologue into a modern, open-ended means of self-expression.

Gray, whose body has been retrieved from the East River in New York two months after he disappeared from his Manhattan apartment, was a prism of extreme behaviour in the world around him. He walked many edges, so many you could be grateful he lasted as long as he did - or be suspicious that he is not dead at all, that this is an elaborate scheme allowing him to attend his own funeral and write a monologue about it.

The latter scenario would be vintage Gray - he was part social scientist, as well as his own guinea pig - but not, from the tone of family reports, the man he had become since a car accident in Ireland in 2001. He suffered leg injuries that required extensive surgery and left him, by his own description, humourless and depressed.

Late last year, he gave some workshop performances of a new monologue that documented the event, but he was also reported to have attempted suicide in 2002, and was said to have been on anti-depressant drugs. Ironically, this decline came at a time when, after a series of long- and short-term relationships, he had married Kathleen Russo, had two children, settled in scenic North Haven, Long Island, and taken up the surprisingly conventional pastime of skiing.

However witty Gray's work was, there was always a dark undercurrent in his dozen or so monologues, and a quirky sensibility in his 30-plus film roles. In his book, Impossible Vacation (1992), he recalled a suicidal moment during his teens, when he considered jumping out of a window. "I figured I'd just break a leg or something, and end up in a cast for the rest of the summer ... Then I also realised that mom [who was to commit suicide at the age of 52] wouldn't be able to give me any attention, because she was cracking up and needed all of it for herself."

Raised in Providence, Rhode Island, as a Christian scientist, Gray was plagued by dyslexia, and was in boarding school for two extra years before attending Emerson College, Boston. Though he had traditional acting training at the Alley theatre, in Houston, he gravitated towards avant-garde theatre in New York in 1967, and was a founding member of the progressive Wooster Group. During this period, he could not afford to own a television, and found that giving a chronicle of his day gave shape to his life: "The ritual of that was extremely satisfying."

His monologues grew out of improvisation, starting with Sex And Death To The Age Of 14 in 1979, but his breakthrough came after a minor role, as the US consul in The Killing Fields (1984), which yielded the monologue Swimming To Cambodia, later filmed by Jonathan Demme in a work that consisted almost entirely of Gray sitting, standing and talking. The play focused on the filmmaking process, but also explored US responsibility for the ravages in Cambodia and truths about Gray's own perceived failures and darkest personal secrets.

Other monologues, including Terrors Of Pleasure (1988), Monster In A Box (1992) and Gray's Anatomy (1996), were also filmed, and often produced by Renee Shafransky, who was his companion for 13 years prior to his marriage to Russo.

Gray also made numerous brief film appearances, including Beaches (1988), Beyond Rangoon (1996), Kate And Leopold (2001) and The Paper Mache Chase (2003), plus the recurring role of Dr Jack Miller in the popular American television sitcom The Nanny, to maintain what he called "horizontal celebrity" - a low, but consistent, level of recognition that allowed him to support his family, keep up his health benefits and continue writing his monologues for a smaller audience. At times, he would arrive on the set of a high-profile Hollywood film with his co-stars forbidding him to portray them in his monologues.

In fact, the monologues rarely involved anything so conventional as a film star. Rather, they constituted a fringe history of 1980s and 90s America. Many were picaresque travelogues over many locales, from lavish lunches with vapid Hollywood executives, in Monster In The Box, to the traumas of eye surgery, in Gray's Anatomy, to interviewing the Dalai Lama for a Buddhist publication.

Gray often cast himself as a passive figure, simply reporting what had happened to him, almost as a lightning rod of the zeitgeist. But he admitted that he sought out strange experiences so as to report on them. They could be clubs of UFO watchers or native American peyote rituals. In conversation, he would casually mention, "I've drunk my own urine. I have."

Such experiences were not always enviable. And though he embodied the stereotype of the self-absorbed New Yorker - looking at the world through the lens of one who had known intensive psychotherapy, fad diets and mind-expanding drugs - his pursuit of a story had a degree of selflessness that often put the amiable, all-too-accessible Gray in harm's way.

Though he drew equally from standup comedy, performance art, bedtime storytelling and classroom lectures, he mainly described his work as journalistic. After Swimming To Cambodia, however, he increasingly abandoned the idea that a given piece was about a discrete event. They covered a particular time frame in his life, but ended inconclusively, though with a definite feeling that the subjects at hand had been fully explored.

Gray admitted that his work was not scrupulously factual. He played fast and loose with the order of events. The more fantastical manifestations of his neuroses - during one anxiety attack, he claimed, he sweated through his shoes and left wet footprints - were often fabricated.

"I am interested in what happens to the so-called facts after they have passed through performance and registered on my memory," he once said. In another interview, he provocatively compared himself to a collage artist who "cuts and pastes his memories". The best moments of his writing also involved unlikely juxtapositions of imagery. He likened his unpleasant experience smoking marijuana in Thailand, for example, to being trapped in "a demented Wallace Stevens poem, with food poisoning".

Gray's dyslexia made him loath to commit his monologues fully to paper. The notebook in front of him contained mostly key words. Though he usually developed a set text for any given piece, his monologues were indeed a performance that came about from reliving a succession of visual images at every performance.

Kathleen and their sons, Forrest and Theo, survive him. David Patrick Stearns

Jon Blair writes: The first time I met Spalding, it was difficult to see how he had survived that long. To say that his ego, id and whatever else made up his personality, were raw and out there, permanently on display, would be to understate things monumentally. Here was a man who not only made his living telling audiences, night after night, quite hilariously, about his hang-ups and neuroses, but who actually was as he described himself.

It was New York in early 1991, and I had raised the money to finance a film production of Monster In A Box, the sequel to his masterpiece, Swimming To Cambodia. Like Swimming, Monster dealt with the inner demons that tortured Spalding in his daily life, this time themed around the troubles he was having condensing and finishing his first novel (the eponymous Monster of the monologue's title).

On stage, his style ranged from throwaway to hysteria, but off stage Spalding spoke quietly and drank copiously: not the water that, together with a desk and a chair, were his only stage props, but vodka. But whether in front of a paying audience, or in a restaurant with friends, he, and you, could never get away from the narcissistic self-absorption and neuroses that were both the source and the fuel for his brilliant monologues.

When we first met, Spalding was approaching 50, and, even then, he was dominated by his mother's suicide. In fact, Monster In A Box begins with the line, "You see in 1967, while I was trying to take my first vacation, my mother killed herself." Spalding believed he would not survive his own 52nd birthday, for the suicidal demons, even then, were toying with him - or was it he with them?

Of course, he did survive that anniversary, but, one way or another, he always seemed to be drowning. Here, for example, in his own words, is a description of the poster for Swimming To Cambodia: "It is a picture of my head with a very distressed expression, and the waterline is right here [indicating just below his nose], and I'm either coming up, surfacing from the water, or going down for the last time, depending on how you look at it."

So, did he welcome the icy waters of the East River, as he finally showed us which way he viewed that image on the poster? I hope so, and I hope it was not just the despair and the depression that everyone talks of. Even now, I can picture Spalding on stage, flowing silver mane, check lumberjack shirt, glass of water (or is it vodka?), making us laugh till we cry as he tells the gloriously crafted tale of the night he jumped from the Staten Island ferry, and finally found "the perfect moment", to the pursuit of which his lifetime had seemingly been devoted.

· Spalding Gray, writer and performer, born June 5 1941; died before March 7 2004